Vibrio cholerae O1 is the causative agent of pandemic cholera, a severe diarrheal disease still prevalent worldwide. The major etiologic agent of the Seventh Cholera Pandemic that began in 1961 and continues today is the cholera toxin producing El Tor O1 strains. These strains were first thought to have low virulence potential as they cause disease of less severity than "classical" strain responsible for earlier pandemics. However, the lowered virulence of El Tor strains is believed to have contributed to their pandemic spread since a majority of infected persons do not become ill but do become colonized and excrete the infectious organisms. Indeed, one factor thought to contribute to the emergence of El Tor strains is their ability to persist an average of 5 days in asymptomatic carriers compared to only 1.5 days for classical strains. Thus, El Tor strains have genetic factor(s) absent in classical strains that contribute to prolonged colonization. These genetic factors had not been previously identified. Using a new animal model of cholera amenable to studies of the host immune response, we have demonstrated that accessory toxins hemolysin and RTX are key factors in establishment of prolonged V. cholerae colonization of the crypts of the small intestine. This grant will continue examining the connection between hemolysin, RTX and innate immunity using coinfection studies to determine if colonization defects can be extracellulary complemented. This study will also investigate the cell types recruited to the gut associated lymphoid tissue during early V. cholerae infection. Finally, this project will specifically determine whether neutrophils and mast cells are key components of the innate immune response to V. cholerae and whether these cells are disabled by hemolysin and RTX toxin both in vivo. PUBLIC HEALTH RELEVANCE: Vibrio cholerae O1 is the causative agent of pandemic cholera, a severe diarrheal disease still prevalent worldwide. The epidemiology of modern cholera is distinct from the Classical disease as epidemics are caused by lower virulence strains that induce a high frequency of mild or asymptomatic infections. This prolonged period of vibrio excretion likely contributes to transmission of disease. Using a new animal model of cholera, accessory toxins hemolysin and RTX are shown to be key factors in prolonging intestinal colonization by V. cholerae. This project will investigate key components of the immune response to V. cholerae and identify is accessory toxins are associated with disabling innate immunity.